Signal receiving system



Aug. 8, 1933. H. R. HAYDEN SIGNAL RECEIVING SYSTEM .QNN R Y. fi NNN E; m Wu 0.3m .%\N\ Nm m d MM @N d m N f HB@ www .KN MRNN m NNW 9 @A E. E. a? m NNN SQ e, 4# N m ISQN wf l I, m mi n N N Qww A w@ Q g g f Patented Aug. 8, 1933 'UNITED STATES PATENTE OFFICE 2 Claims.

This invention relates to electrical systems employing vacuum tubes as repeaters or amplifiers and particularly to vacuum tube signal receiving systems.

'I'he system herein illustrated is a multi-stage signal receiving system employing a plurality of stages of radio frequency amplification, a detector stage and a plurality of stages of audio frequency amplification, the last stage serving to operate a loud speaker or other translating device. Each stage of the system includes a threeelectrode tube, the plate circuit of which is energized from a source of fluctuating direct current, such for example as from an alternating current supply system through a rectifierl and ilter. Provision is made also 'for heating the filament or cathodeof the tube by a fluctuating or alternating current flowing through the filament or heating element of the tube. Furthermore in the system herein disclosed means is provided for supplying the requisite grid biasing voltages for the several tubes from the source of current for the plate circuits.

The use of alternating current as a source of supply for the tube circuits tends to create disturbing current variations in the output circuit of the last tube, thus interfering with the satisfactory reception of signals. Thus with the plate circuits of the tubes supplied from the source of alternating current through a rectier and filter, the current supplied to the plate circuits, although unidirectional, is subject to variations of low frequency which tend to produce a disturbing noise or hum in the loud speaker. This effect is more pronounced in systems employing a plurality of audio frequency stages arranged in tandem and coupled to one another by audio frequency couplings, because the low frequency hum variations in the plate circuits of .the rst stages are readily carried over through the audio frequency couplings to the grid circuits of succeeding stages and are amplied in the succeeding stages. Also when alternating current isemployed in the filaments of the tubes the alternate heating and cooling ofthe filament as well as the electromagnetic and electrostatic eil'ects prbduced by the alternating current in the filament tends to cause disturbing current variations in the tube plate circuits and this tendency also is more pronounced in the case of` multistage audio frequency amplifiers.

One important object of the present invention is to provide a system of this general character wherein a source of fluctuating current is employed for energizing one or more of the tube circuits and wherein disturbing current variations in the plate circuit of the last stage are substantially reduced or eliminated. A further object of my invention is to provide an improved system wherein all the tube circuits are supplied (Cl. Z-27) from a source of alternating current thus avoiding the `use of batteries and at the same time disturbing variations in the plate circuit of the last tube are substantially reduced or eliminated.

A further object of my invention is to provide a vacuum tube signal receiving system having its parts so constructed and arranged that the tube circuits may be supplied from a source of fluctuating current or potential andthe disturbing effects caused by the fluctuations in the supply will be balanced out in the system so that little or no disturbingvariations will occur in the plate circuit of the last tube.

In systems constructed in accordance withd my invention, which are designed to eliminate hum, I make use of an interstage coupling so constructed and arranged that disturbing current variations in an earlier stage are reversed and the reversed variations are caused to oppose in their effects the effect of similar disturbing current variations in a later stage. In the form of invention illustrated in the drawing I employ for accomplishing this result in the audio frequency part of the system resistance couplings, although I may employ reactance or impedance couplings such as disclosed in my copending application Serial Number 337,294, led February 4, 1929, of which this application is a continuation in part. In certain cases also I may employ direct couplings or other types of couplings constructed to effect the reversal of phase above mentioned.

In the operation ofthe system employing resistance couplings, as herein illustrated, these couplings serve to impress on the grid of the following tuber potential variations which are dependent upon potential variations at some point in the plate circuit of the preceding tube. By proper construction and arrangement of the. couplings or of the circuits with which `said couplings are connected, I am able to cause variations in a preceding stage to oppose and reduce similar variations arising in a succeeding stage. A further object of my invention rtherefore is to provide a system of this character wherein variations arising in or impressed upon differentstages are caused to oppose or neutralize one anotherso that no appreciable disturbing hum. occurs in the loud speaker.

Further features of my improved signal receiving system include high selectivity in tuning for the reception of signal waves of diierent frequency, a maximum amplication of the received signals, a minimum expenditure of power in the receiving circuits, the reproduction of the received signals without substantial distortion and the elimination of disturbing current variations due to regeneration or similar effects. v

A further object of my invention is to provide a vacuum tube receiving system which may be energized from any suitable source of current such as an alternating `current house lighting system and wherein provision is made for automatically compensating for fluctuations or variations in the voltage of the source of supply,

.as will be more fully explained hereafter.

Other objects and advantages of my invention will appear from the following description taken in connection with the accompanying drawing which shows a circuit diagram of a signal receiving system embodying one form of my in- Vention.

In the drawing-reference character 10 represents an antenna adapted to receive signal waves. 'Ihe antenna is grounded at 11 through the primary 12 of a radio frequency transformer 13, the secondary 14 of which is in the grid circuit of the first radio frequency amplifier tube 16. Connected across the terminals of the Winding 14 is a condenser 18 which is adjustable to tune the grid circuit of tube 16 to the frequency of signals to be received. For the purpose of providing a ner tuning adjustment I may if desired employ a smaller condenser 19 in shunt to the condenser 18. The grid of tube 16 is grounded through conductors 25, 26, and 27. I may if desired employ an adjustable resistance 30 connecting the plate and grid of tube 16 which resistance acts as a stabilizer.

The plate circuit' of tube 16 is coupled to the grid circuit of the second radio frequency amplier tube 34 by a transformer 35 having a primary 36 in the plate circuit of" tube 16 and a secondary 38 in the grid circuit of tube 34. Tuning condensers 39 and 40 are connected in the grid circuit of tube 34, across the secondary winding, 38 and this grid circuit is grounded through conductors 26 and 27. I may also employ a stabilizer 42 connecting the grid and plate of the tube 34.

The plate circuit of tube 34 includes a winding 44 in inductive relation to a winding 45 in the grid circuit of the detector tube 47 andI this grid circuit includesthe tuning condensers 48 and 49 connected across the terminals of winding 45. Winding 45 and condensers 48 and 49 are connected to the grid of tube 47 through an adjustable condenser 50 of small capacity "and in parallel with condenser 50 a high resistance 51 which is also adjustable. The grid circuit of the detector tube 47 is ygrounded through conl ductors 54 and 27.

Connected in series with the plate of detector tube 47 is a winding 55 positioned in inductive relation to the grid circuit winding 45. Winding 55 is adjustable relative to winding 45 so as to alter the mutual inductance between the two windings.

The windings 44, 45, and 55 form a so called three-circuit tuner and these windings are preferably constructed and arranged as described in my copending application Serial Number 196,244, filed June 8, 1927. The radio frequency transformers 13 and 35 may be of similar construction such a.; is described in said application. In certain cases, particularly when employing radio frequency transformers of the constructions specified in said application, I find it advantageous to include in the plate circuits of tubes 16 and 34, small reactances 58 and 59 of Say 85 millihenrys and an inductance 60 of approximately the same value in the plate circuit of the detector tube.

The plate circuit of the detector tube 47 is coupled to the grid circuit of the first audio frequency amplifying tube 62 through a resist.

The grid circuit of the second audio frequency amplifying tube 74 is connected to the plate circuit of tube 62 by a resistance coupling 75 comprising a resistance 76, a resistance 77, and condenser 78 connected as shown. Similarly, the grid of the amplifier tube 80 which in the system shown is in the last stage of amplification is coupled to the plate circuit of tube 74 by a resistance coupling 82 comprising a resistance 83, resistance 84, and condenser 85. 'Ihe highly amplified currents in the plate circuit of the nal amplifier tube 80 serve to operate a loud speaker or other signal translating device 90. The loud speaker may be shunted by a condenser 91 of small capacity. If desired, the resistance 84 of the coupler 82 may be shunted by a resistance 93 which is adjustable to control the volume of sound in the loud speaker.

The filaments or cathodes of the several tubes are heated by alternating current derived from the alternating current supply system 100. The cathodes or-1aments of the radio frequency and audio frequency amplifier tubes are directly heated by alternating current passed therethrough. 'I'he detector tube 47, as shown, is of the indirectly heated type and comprises the heating element 101 located closely adjacent to the tube cathode.

Heating current for the filaments of the amplifying tubes is supplied from a secondary 102 y of a step-down transformer 103, the Aprimary 104 of which is connected across the supply mains 100. Connected across the secondary winding 102 is a `potentiometer resistance 106 along )which is slidable a contact 107 connected to the conductor 108. Conductor 108 is grounded through an adjustable resistance 109 of, say 1,000 ohms, maximum, and shunting 'the resistance 109 is a high capacty condenser 110, say of one or4-` more microfarads. The potentiometer resistance 106, tap 107x and conductor 108 form part of the plate return circuits from the filaments of the amplifier tubes and the resistance 109 is employed for supplying tothe grids of the amplifier `tubes the requisite bias:- ing potential, as will be more fully explained hereafter.

The heater 101 of the detector tube 47 is supplied with alternating current from a secondary 112 oi.' the' transformer 103 and connected across the terminals of the secondary 112 is a potentiometer resistance 114 along which is slidable a tap 115 connected to the conductor 116 which is connected to Ythe positive terminal of the plate current supply for the detector tube. The detector tube cathode is grounded through a conductor 117 and an adjustableresistance 120 of say 100,000 ohms maximum, which resistance is shunted by a condenser 121 of high capacity, say'- one microfarad.

For the purpose of supplying direct' current for energizing the plate circuits of the tubes, I provide a rectifier 130 adapted to be energized from the alternating current mains 100 and connected with the output circuit of the rectifier a filter 132.

Reference character 133 represents the primary of an alternating current transformer 134 supplied from the mains 100 and reference characters 135 and 135a represent respectively high and low voltage secondaries of the transformer 134. The rectifier 130 in the form of invention disclosed comprises a vacuum tube 136, the plate and grid of which are connected to one terminal of the secondary 135 and the filament of which is connected across the secondary winding 135a through a current controlling rheostat 137. The other terminal 140 of the secondary Winding 135 forms the negative terminal of the B supply and is grounded through conductors 141 and 27. One terminal of the secondary 135a is connected\ through a reactance coil 142 of relatively high impedance to the conductor 144 which forms the positive terminal conductor of the filter. Connected across the filter output circuit at opposite sides of the reactance 142 are high capacity condensers 146 and 147 and also connected across the output circuit between the conductors 144 and 141 are three parallel circuits each comprising adjustable resistances 150, 151, and 152, respectively, of relatively high value and in series with each resistance a high capacity condenser 153, 154, and 155, respectively. 'Ihe rectifier and filter, it will be seen, are of similar constructions to those disclosed in my copending application Serial Number 337,- 294. above referred to, and I find that in the filter I may use condensers of correspondingly low capacities.

Leading from a point between theresistance 152 and condenser 155 is a conductor 160 which connects through the resistance 64, reactance 60 and tickler coil 55 to the plate of the detector tube.

Leading from .a point between the resistance 151 and condenser 154 is a conductor 162 which, as shown, supplies the plates of the radio frequency amplifier tubes 16 and 34.

Leading from a point between the resistance 150 and the condenser 153 is a conductor 164 which supplies current to the plates of the three audio frequency amplifier tubes. When a power tube is used I mayxif desired supply the plate of the power tube with current from the terminal 144. The plate circuit of tube 47 is customarily supplied with relatively low voltage. When I employ a tube of the indirectly heated type, such for example as the so-called 327 tube, I may use a plate voltage in the neighborhood of 15 volts and with such tube I find that the resistance 120 may advantageously be, say 10,000 to 100,000 ohms, and with a correspondingly high grid leak resistance 51. The radio frequency amplifier tube plate circuits would ordinarily be supplied with current at a somewhat liigher voltage than that supplied to the plate circuit of the detector tube and the plate circuits of the audio frequency amplifier tubes be supplied with still higher voltage. When employing as amplifier tubes the so called 326 tubes I may employ as a resistance 109 an adjustable Iresistance of 1,000 ohms maximum. It will, however, be understood that I may use tubes of different types and the designation of the tubes above specified and tubes at less filament current than that for which the tubes are designed and at a reduced plate voltage without materially affecting the volume.

From the above description it will be seen that the filaments of the several amplifier tubes are supplied in parallel with one another from the secondary 102 of the transformer 103 and the heating element 101 of the detector tube is supe plied from the secondary 112 of the transformer 103. The plate circuits of the several tubes may be easily tracedl on the drawing. Thus the plate circuit of the first audio frequency amplifier tube 62 may be traced from the positive conductor 144 of the filter, through resistance 150, conductor 164, coupling resistancel76 to the plate of the tube 62; thence to the filament of tube 62 through the filament supply circuit to the potentiometer 106; thence to the slider 107 through conductor 108, resistance 109, through conductors 27 and 141 to the negative terminal 140. The plate circuit of the detector tube may be traced from positive supply conductor 144, resistance 152, conductor 160, coupling resistance 64, inductance 60, tickler coil 55, to the plate of detector tube 47; thence to the cathode of the detector tube, through conductor 117, adjustable resistance 120, conductorsv 27 and 141, to the negative terminal of the B supply.

In my copending application Serial Number 299,680, filed August 15, 1928, I- disclose a vacuum tube resistance coupled amplifier, the plate circuits of which may be supplied with fiuctuating direct current and wherein means is provided for substantially'reducing or eliminating disturbing current variations in the plate circuit of the last amplifier tube. In my copending application, Serial Number 337,294, filed February 4, 1929, I also explain how disturbing current variations derived from the use of alternating currents in the tube filaments may be caused to oppose one another in the last stage of amplification, so as to substantially reduce or eliminate disturbing current variations from this latter source in the plate circuit of the last tube. In considering the opposing effects due to the alternating filament currents merely in two successive stages, such as two audio frequency resistance coupled stages, if dVf represents the change in potential of that point in the plate circuit of the first stage, which is connected to the coupling condenser, then the change in voltage of the corresponding point in the plate circuit of the next stage, due to dVf will be Io [1F dVfrp +r where ro is the coupling resistance or impedance in the plate circuit of the second tube and rp is the impedance of the second tube. This effect will be opposed by the effect dVzf of the alternating current in the filament of the second tube.

In my application Serial Number 337,294, I

also disclose how any residual disturbing cur-- rent variations derived from the fluctuating B supply or the alternating current `A supply may be made to oppose or substantially cancel one another. In'systems constructed in the manner herein set forth I am able effectively to so reduce the disturbing current variations that no disturbing hum occurs in the loud speaker and I am also able to prevent the occurrence of disturbing regenerative effects which are so common in resistance coupled amplifiers. In my earlier applications above referred to I describe a number of adjustments which are effective in securing the desired elimination of hum in the loud speaker. Similar adjustments in the present system are also effective to this end. More important among these adjustments are the adjustments of resistances 170 in the filament supply circuits. In the form of invention illustrated in the drawing separate resistances 170 are provided in one leg of each filament and also in one leg of the heater 101 of the detector tube.k Adjustment of these resistances serves not only to control the current through the laments but also changes the potentials of the grids with reference to the mid-point of their respective filaments. I also find that .adjustment of the slider 107 is eifectivein securing the desired elimination of hum as is also adjustment of resistances 51, 109, and 120.

A further feature of advantage in the present system resides in the use of resistances 109 and 120 and the shunting of `these resistances by condensers 110 and 121. These resistances are employed to provide requisite negative bias on the grids of the several tubes. It will be noted in the system illustrated that the grids of all tubes are connected to -B through conductors 27 and 14,1; that the plate return circuits of all the amplifier tubes are connected to .-B through the resistance 109 and that the plate return circuit from the detector tube is connected to -B- through resistance 120. It therefore follows that the grids of the amplifier tubes have a negative bias proportional to the ir drop through resistance 109 and the grid of detector tube 47 has a bias proportional to the ir drops in the resistance 120 and the grid leak resistance 51.

The shunting condensers 110 and 121, each, serve as a b v-pass for the signal currents. Without these condensers the signal currents would be reduced due to the higher impedance of the circuitsthrough which they flow and also because the resistances in the plate return .circuits form a negative or anti-oscillatory feedback connection between the plate and grid circuits.4 Thus on increase in plate current of a tube, due to positive incoming signal impulse, the voltage drop across the resistance increases, making the grid of that tube less positive and thus neutralizing part of the incoming signal. The shunting condensers, while not changing the direct current biasing potential, offer a path of low impedance for the signal frequencies.

I do not find in the case of resistance coupledl amplifiers that it is necessary to use by-pass condensers of very large capacity, particularly with relatively low plate circuit-voltage. It is to be noted that the resistance 109 is common to the return circuits of all the amplifier tubes. With the audio frequency tubes coupled by resistance couplings, an increase in the signal current in the plate circuit of one tube is accompanied by a decrease in the signal current in the plate circuit of the next tube. There is therefore a tendency for the combined plate currents of these tubes to remain constant and so to minimize the tendency to negative feed` back. I find in the system illustrated that bypass condensers of one or two microfarads give excellent results. The resistances 109 and 120 have a further advantage in that they compensate for fluctuations in potential of the supply mains 100.. Thus if the voltage of the supply mains 100 rises, say from 110 volts to 120 volts. there is a tendency to increase the plate current. However, any increase in plate current `produces a less positive bias of the grids, which Utends to offset the increase in plate current.

One embodiment of my system, using impedance couplings instead of resistance couplings, is the same as that shown in the drawing except that coupling impedances are substituted for the resistances '76 and 83 and a coupling impedance is substituted for the resistance 64 and condenser 70. In such system I may if desired omit the reactance 60.

Having now described my invention, what I- claim and desire to secure by Letters Patent is:

1. A vacuum tube signal receiving system having a radio frequency amplifying portion, a detector stage and an audio frequency amplifying portion comprising resistance coupled stages; the amplifying portions having a'common plate circuit return including a relatively low resist- 'ance and the detector stage having a plate circuit return including a relatively high resistance; connections'between the grid of each tube and the negative side of the resistance in the plate circuit ofsuch tube; high capacity condensers shunting the respective resistances, means for supplying the plate circuits with direct current potential which is subject to occasional variations which tends to create disturbing variations in the plate circuits, means for heating the cathodes of the tubes by current subject to variations which tends to create disturbing variations in the plate circuits, means for causing the variations applied to the earlier stages and carried forward-through the interstage couplings and thereby affecting the grid of a later stage to oppose at a resistance coupling variations supplied to a later stage and means for causing the values of the. opposing effects to bear a predetermined relation one to the other.

2. A vacuum tube signal receiving system having a radio frequency amplifying portion, a detector stage and an audio frequency amplifying portion comprising resistance coupled stages; the amplifying portions having a common plate circuit returnV including a relatively low resistance and the detector stage having a plate circuit return including a relatively high resistance; connections between the grid of each tube and the negative side of the resistance in the plate circuit of such'tube; high capacity condensers shunting the respective resistances, means for supplying the plate circuits withA direct current which is subject to occasional variations which tends to create disturbing variation in the plate circuits, means for heating the cathodes of the tubes by current y subject to variations whichtends to create disturbing variations in the plate' alater stage and means for causing the values of the opposing effects to bear s uch relation to one another that disturbing variations in the output circuit are substantially eliminated.

' V' HAROLD R..HAYDEN. 

